Automatic sensitivity-regulating device

ABSTRACT

Automatic sensitivity-regulating device, characterized by the fact that it has two sensitivity recovery time constants, one a slow one which is applied permanently in case of the presence of a signal and the other a rapid one which is placed in operation if the signal remains less than a selected level during a selected period of time.

United States Patent Inventor Stefan Kudelski CH. de la Croix-l052 LeMont-sur- Lausanne, Chemin de la Croix, Switzerland Appl. No. 887,302Filed Dec. 22, 1969 Patented Nov. 2, 1971 Priority Dec. 26, 1968Switzerland 19,289/68 AUTOMATIC SENSITIVITY-REGULATING DEVICE 6 Claims,3 Drawing Figs.

Int. Cl l-l03k 17/28 Field of Search 307/293;

[56] References Cited UNITED STATES PATENTS 2,719,226 9/1955 Gordon etal 328/120 X 3,019,396 l/1962 Heine et al 330/28 3,068,367 12/1962 Brownet al 328/120 3,119,970 1/1964 Thompson et al. 330/138 X 3,202,9298/1965 Benger etal 330/138 3,284,713 11/1966 Bailey 330/138 X PrimaryExaminer-Donald D. Forrer Assistant Examiner-R. C. WoodbridgeAttorneys-James M. Heilman and Heilman & Heilman ABSTRACT: Automaticsensitivity-regulating device, characterized by the fact that it has twosensitivity recovery time constants, one a slow one which is appliedpermanently in case of the presence of a signal and the other a rapidone which is placed in operation if the signal remains less than aselected level during a selected period of time.

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This invention relates to a variable impedance, and more particularly,to a variable impedance device providing different recovery timeconstants.

It is known that a microphone supplies a signal which is proportional tothe acoustic levelwhich it picks up. This level may vary within wideproportions in actual sound recording and to a lesser extent in the caseof a telecommunications transmitting microphone. Now, in order to recorda signal or modulate a transmitter, it is necessary to have signallevels which are relatively constant. Regulation can be effectedmanually by means of a potentiometer and a voltmeter which measures theamplitude of the signal or automatically by means of a device whichmeasures the amplitude of the signal and acts on a variable gain device.The known automatic regulators in general comprise a memory whichordinarily consists of a capacitor, the gain being'related to thevoltage to which said capacitor is charged. The charging of thiscapacitor, which corresponds to a decrease in gain, takes place veryrapidly so that the first syllable of a word is regulated, but therecovery time is much slower, presenting certain problems. If one uses arapid recovery time, the sensitivity increases between the words, andthis results in a very disagreeable effect due to increase in thebackground noise between the words. If the time constant is long, thatis, the recovery time is slow, this phenomenon is no longer disturbing,but the readaptation of the gain to a weak signal which may have beenpreceded by a strong signal, is too slow.

SUMMARY OF THE INVENTION In order to overcome these drawbacks, an objectof the present invention is to provide automatic sensitivity regulatingdevice which is characterized by the fact that it has two sensitivityrecovery time constants, namely, a slow one which is applied permanentlyin case of the presence of a signal, and the other a rapid one which isplaced in operation if the signal remains below a selected level duringa selected period of time.

Another object of the present invention is to provide an improvedautomatic sensitivity regulating device.

FIGURES FIG. 1 is a schematic diagram of the present invention; FIG. 2is an explanatory graph therefor;

FIG. 3 is a schematic diagram of a detail of FIG. 1.

DETAILED DESCRIPTION In the arrangement shown in FIG. 1, an input signalis applied in the form of current to terminals 23, 26, through a seriesconnection of resistor 8 and capacitor 9 to a device 10, the impedanceof which varies as a function of a control voltage E which is applied toanother input 25 of device 10. As soon as the voltage E exceeds a giventhreshold value, for instance 3 v., the impedance decreases, forinstance by 6 db. per 95 v. applied. The signal affected by the variableimpedance 10 is supplied to an amplifier ll. phase shifter 12 located atthe output of amplifier l 1 comprising a relatively standard capacitorresistor combination enables the signal amplified by amplifier 11 to beprovided as two equal signals in phase opposition. The first of thesetwo signals is supplied to the base of transistor T,, while the other isapplied to the base of transistor T,. Transistors T, and T, forma peakrectifier l3 and a capacitor C, connected between their interconnectedemitters and a point of reference potential is charged to a voltage, thevalue of which is related to the peak voltage of the input signal. Thisvoltage on the capacitor C, constitutes the control signal E of thevariable impedance 10. The capacitor C, is discharged by the resistor R,of high value, which causes this discharge to be slow and to lastseveral seconds (slow recovery, for instance I to 2 db. per second onthe average).

Simultaneously, the presence of a signal of sufiicient amplitude iscoupled to the base of transistor T through capacitor C, and causes thetransistor T to conduct and discharge the capacitor C, which isconnected to the collector of transistor T The base of transistor T. isconnected to the collector of transistor T and upon the discharge ofcapacitor C, is rendered nonconductive. If the amplitude of the signaldrops below the value necessary to make the transistor '1', conduct, theresistor R connected between the collector of T, to a source ofreference potential charges the capacitor C, and, at the end of a periodof time t, (FIG. 2), the transistor T starts to conduct and rapidlydischarges the capacitor C, through the resistor R (rapid recovery, forinstance 10 db. per second).

The graph of FIG. 2 illustrates this operation and shows the decrease ofthe gain at the time of the appearance of the signal, its slow increaseduring the time t,, and its rapid increase subsequently.

The variable impedance device 10 can be developed in the manner shown inFIG. 3. In this circuit, 21 is a diode bridge constituting a variable,nonlinear impedance, 22 is a positive source of potential, 23 the signalinput, 24 the signal output, 25 the terminal for the application of thecontrol voltage, 26 the common ground terminal, 27 and 28 thetransistors T, and T, respectively, and 29 a logarithmic circuit. Thediagram also shows the currents I, and I the current I the directcurrent I controlled establishing the operating point and the constantalternating current I What is claimed is:

1. An automatic sensitivity regulating device responsive to the leveland duration of an input signal comprising:

a. an input circuit including a series resistor;

b. an amplifier coupled to the input circuit for receiving andtransmitting a signal;

c. a variable impedance circuit connected to the input circuit forvarying the amplitude of the signal applied to the amplifier, saidvariable impedance including a control terminal, the voltage of whichdetermines the circuit impedance;

d. A capacitor coupled to the amplifier output terminals and to saidcontrol terminal, said capacitor chargeable to a DC voltage responsiveto the input signal;

e. a first resistor connected across said capacitor for discharging itat a first predetermined rate;

f. a second resistor coupled to the capacitor in series with atransistor for discharging the capacitor at a second predetermined rate;

g. and a coupling circuit between the amplifier output and thetransistor for making the transistor conductive when the input voltageexceeds a predetermined value, thereby permitting current to flowthrough the second resistor.

2. A regulating device according to claim 1 wherein said variableimpedance circuit includes a four armed bridge circuit having a dioderectifier in each of its four arms.

3. A regulating device according to claim 2 wherein said bridge circuitis connected to a transistor having base, collector, and emitterelectrodes, said collector and emitter electrodes connected in serieswith the bridge, and the base connected to said control terminal.

4. A regulating device according to claim 1 wherein said amplifiercircuit includes output terminals connected to a pair of phase-shiftingmeans with the first of said pair providing a first phase shift and thesecond of said phase-shifting means providing a second phase shift, saidsecond phase shift being complementary to said first phase shift.

5. A regulating device according to claim I wherein said transistor inseries with the second resistor is normally nonconducting and is madeconducting by a voltage derived from the output of said amplifier.

6. A regulating device according to claim 1 wherein the output terminalsof said amplifier are connected to a full wave rectifier for chargingsaid capacitor.

n a s s a

1. An automatic sensitivity regulating device responsive to the leveland duration of an input signal comprising: a. an input circuitincluding a series resistor; b. an amplifier coupled to the inputcircuit for receiving and transmitting a signal; c. a variable impedancecircuit connected to the input circuit for varying the amplitude of thesignal applied to the amplifier, said variable impedance including acontrol terminal, the voltage of which determines the circuit impedance;d. A capacitor coupled to the amplifier output terminals and to saidcontrol terminal, said capacitor chargeable to a DC voltage responsiveto the input signal; e. a first resistor connected across said capacitorfor discharging it at a first predetermined rate; f. a second resistorcoupled to the capacitor in series with a transistor for discharging thecapacitor at a second predetermined rate; g. and a coupling circuitbetween the amplifier output and the transistor for making thetransistor conductive when the input voltage exceeds a predeterminedvalue, thereby permitting current to flow through the second resistor.2. A regulating device according to claim 1 wherein said variableimpedance circuit includes a fOur armed bridge circuit having a dioderectifier in each of its four arms.
 3. A regulating device according toclaim 2 wherein said bridge circuit is connected to a transistor havingbase, collector, and emitter electrodes, said collector and emitterelectrodes connected in series with the bridge, and the base connectedto said control terminal.
 4. A regulating device according to claim 1wherein said amplifier circuit includes output terminals connected to apair of phase-shifting means with the first of said pair providing afirst phase shift and the second of said phase-shifting means providinga second phase shift, said second phase shift being complementary tosaid first phase shift.
 5. A regulating device according to claim 1wherein said transistor in series with the second resistor is normallynonconducting and is made conducting by a voltage derived from theoutput of said amplifier.
 6. A regulating device according to claim 1wherein the output terminals of said amplifier are connected to a fullwave rectifier for charging said capacitor.